The present invention claims priority from Japanese Patent Application No. 1004668 filed Feb. 11, 1998, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a detection circuit for detecting the state of use of B channel of an Integrated Services Digital Network (ISDN) and an ISDN terminal equipment including the detection circuit and, particularly, a detection circuit for detecting the state of use of B channel suitable to be applied to a terminal equipment in a system in which a plurality of terminal equipments are connected to a single ISDN and the ISDN terminal equipment.
2. Description of Related Art
FIG. 1 is a block diagram showing an example of a communication system to be connected to an ISDN. In FIG. 1, the ISDN is connected to a user side through a network terminal (NT) 100. It is assumed here that the ISDN serves the basic rate interface. In this example, a main control device 200 of a key telephone system and an ISDN multi-function telephone set 300 are connected to a bus 400 on the user side. The main control device 200 of the key telephone system includes an ISDN S/T reference point interface portion 210 which performs a protocol processing of layers 2 and 3, etc., and a key telephone set interface portion 220 which is connected to key telephone sets 231, 232 and 233 and realizes an extension exchange function and a line wire originating/terminating call functions, etc.
In such system, when, for example, the ISDN multi-function telephone set 300 is performing a communication by using the B channel, the main control device 200 of the key telephone system can not recognize that the B channel of the ISDN is being used by the ISDN multi-function telephone set 300. It is usual that each of the key telephone sets 231, 232 and 233 has an office telephone button by which an information of whether or not the two B channels are being used is displayed. Therefore, even when the ISDN multi-function telephone set 300 is using the B channel, the display of the office telephone buttons of the key telephone sets 231, 232 and 233 becomes as if two B channels are being not used. When one of the key telephone sets, say, the key telephone set 232, makes an originating call, the office telephone buttons of the remaning key telephone sets 231 and 233 indicate as if one of the two B channels is used and the remaining B channel is not used. Therefore, the remaining key telephone sets 231 and 233 are allowed to make a call through the remaining B channel and the call may be performed. However, since there is no empty B channel practically. The fact that the use of the network for the originating call from any one of the remaining key telephone sets is impossible is recognized only after an exchange of control messages is performed by using the ISDN and a D channel.
On the contrary, in a case where line wire communications are performed by two key telephone sets through the two B channels, the ISDN multi-function telephone set 300 can not recognize an absence of usable B channel and, therefore, the ISDN multi-function telephone set 300 is allowed to send an originating call. However, when the ISDN multi function telephone set 300 sends the originating call, the fact that the use of the ISDN for the originating call therefrom is impossible is recognized only after an exchange of control messages is performed by using the ISDN and the D channel.
As mentioned, in a case where a number of terminal equipments are connected to the user bus 400 and one of the terminal equipments is using one of the B channels, the remaining terminal equipments can not recognize the fact that the one terminal equipment is using the B channel. Therefore, there may be a case where an originating call from a terminal equipment is allowed even if there is practically no usable B channel. However, such originating call from the terminal equipment can not be connected to a destination. That is, a man-machine interface which is inconvenient for users is employed.
In order to avoid such inconvenience, a system in which the state of use of B channel of one terminal equipment is detected by monitoring and analyzing a content of the D channel for all of terminal equipments including the one terminal equipment on the basis of terminal addresses by using service access point identifiers (SAPI) and terminal end point identifiers (TEI) has been proposed in, for example, Japanese Patent Application Laid-open No. Hei 3-155247. Further, a system in which the state of use of B channel is detected by utilizing a user-user interface served by the D channel and a D channel packet has been proposed in, for example, Japanese Patent Application Laid-open No. Hei 3-96138. Furthermore, a system in which the state of use of B channel is detected by monitoring both the D channel and the B channels and accumulating B channel data after a communication connection through the D channel is confirmed has been proposed in, for example, Japanese Patent Application Laid-open No. Hei 2-239762.
However, in the system disclosed in Japanese Patent Application Laid-open No. Hei 3-155247 in which the processing of the layers 2 and 3 for other terminal equipments must be executed, the load of firmware of the terminal equipment becomes too large to practice this system. On the other hand, the system disclosed in Japanese Patent Application Laid open No. Hei 3-96148 can be totally realized by mounting similar functions on all of terminal equipments connected by the bus and a destination terminal equipment and the system may be realized only limitedly in the ISDN which is a public network. Further, since, in the system disclosed in Japanese Patent Application Laid-open No. Hei 2 239762, data of the B channels must be accumulated in addition to the monitoring of the D channel, the load on the firmware of the terminal equipment is increased and so it is impractically.
In view of the circumstances, an object of the present invention is to provide a detection circuit for detecting the state of use of B channel, with which it is easily possible to judge whether B channels of an ISDN is being used, by using a simple hardware or a firmware.
The detection circuit for detecting the state of use of B channel according to the present invention comprises comparison means for comparing a B channel data of an ISDN with a preset idle pattern and use state output means for supplying a signal indicative of a state of use of B channel on the basis of a result of comparison from the comparison means.
The comparison means may have a construction for either comparing a parallel-converted B channel data with the idle pattern or comparing a B channel serial data with the idle pattern.
The detection circuit further comprises continuity detection means for detecting a continuity of the result of comparison of the comparison means and the use state output means may be constructed such that the continuity detection means outputs a signal indicative of the state of use of B channel when the use state output means detects a continuity of the comparison result.
The detection circuit further comprises pattern setting means capable of setting a plurality of idle patterns and the comparison means may be constructed such that it compares a specific idle pattern output from the pattern setting means with the B channel data.
Further, an ISDN terminal equipment according to the present invention comprises an S/T point interface portion connected to an S/T point interface of an ISDN interface, a terminal control portion for controlling a terminal function and a man-machine interface portion and a detection circuit for detecting a use/non-use of the B channels of the ISDN, wherein the detection circuit comprises comparison means for comparing a B channel data of an ISDN with a preset idle pattern and use state output means for supplying a signal indicative of a state of use of B channel on the basis of a result of comparison from the comparison means.
The terminal control portion may be constructed such that the state of use of B channel in the man-machine interface portion is displayed as being in the use state when an output signal of the use state output means indicates that the B channels are being used and the state of use of B channel in the man-machine interface portion is displayed as being in the non-use when the output signal of the use state output means indicates that the B channels are not used.